1. Field of the Invention
This invention relates to a light-attenuation type fire detector assembly, and more particularly to a light-attenuation type fire detector assembly in which a light emitting section and a light receiving section are disposed so as to oppose each other at a given distance therebetween to form a smoke detecting space between them so that if smoke enters the smoke detecting space, the light receiving section receives light attenuated by the smoke to detect a fire, on the basis of the photo-output from the light receiving station.
2. Relevant Arts
In a conventional light-attenuation type fire detector assembly, a light emitting section for emitting light and a light receiving section for receiving the light from the light emitting section are disposed face to face so as to be spaced by a given distance from each other to form a smoke detecting space therebetween. If smoke enters the smoke detecting space, the light from the light emitting section is attenuated by the smoke and it is detected by the light receiving station. Fire detection is made based on the photo-output from the light receiving section. In such a fire detector assembly, to form an optical path of a required length, 1 m for example, within the limited space of a casing, the light emitted from the light emitting section is reflected several times by mirrors before it reaches the light receiving section. This extension of the optical path provides an effect equivalent to making the smoke detecting space larger. As a result, the attenuation by smoke is increased and the detection sensitivity is increased.
In a light-attenuation type fire detector assembly of this type, however, not only is the emitted light from the light emitting section attenuated by every reflection from the mirrors, but also the attenuation factor is increased due to blurring caused by, dirt or dust build-up etc. on the mirrors. In addition, there is the problem that the optical adjustment mechanism for the mirrors is very complicated and manufacture of the assembly is expensive.
To solve the problems described above, there has been proposed a light-attenuation type fire detector in which a plurality of light receiving sections are provided opposite to and spaced from corresponding light emitting sections, respectively, and which is operated in such a manner that the light emitted from the respective light emitting sections is received by the corresponding light receiving sections. Smoke detection signals indicative of the light attenuation at the respective light receiving sections are integrated by integrating means to determine the amount of smoke so as to obtain, at a reduced cost, an effect equivalent to enlargement of the smoke detecting space.
This type of light-attenuation type fire detector assembly, however, has the problem that it requires a plurality of light emitting sections and an equal number of light receiving sections.
The present invention contemplates a light-attenuation type fire detector assembly which does not use a plurality of light emitting sections and light receiving sections and is capable of reducing the cost and size of the entire assembly.
Prior art relevant to the present invention comprises: U.S. Pat. No. 4,018,534 issued Apr. 19, 1977 to Lawrence B. Thorn et al., U.S. Pat. No. 4,266,220 issued May 5, 1981 to William J. Malinowski et al., U.S. Pat. No. 4,420,746 issued Dec. 13, 1983 to William J. Malinowski et al., U.S. Pat. No. 3,553,462 issued Jan. 5, 1971 to Dennis F. Johnson and U.S. Pat. No. 3,994,603 issued Nov. 30, 1976 to Hansjoachim Paschedag.